Device for monitoring a fluid pressure system

ABSTRACT

A device for monitoring a fluid pressure system comprises a plurality of tranducers for individually detecting local temperatures at a plurality of locations in the system and providing corresponding electric signals, a scanner for addressing the electric signals in accordance with a prescribed program and providing corresponding output signals, a linearizer for calibrating the output signals, an AD converter for converting the calibrated output signals into corresponding digital signals, and means for visually displaying both a temperature characteristic pattern developed from the digital signals and a temperature reference pattern indicative of the acceptable temperature levels in the system whereby a comparison of the two patterns may be made to determine defective components in the fluid pressure system.

United States Patent 1 3,699,810 Takahashi Oct. 24, 1972 [54] DEVICE FORMONITORING A FLUID 3,112,880 12/ 1963 Pollock ..73/341 X PRESSURE SYSTEM3,350,702 10/1967 Herman ..73/355 R X Y 3,474,438 10/ 1969 Lauher..340/324 A [72] Invent fig"; Takahash" 3,473,079 10/1969 Adometto et al..315/25 x [73] Assignee: Japan Aircraft Manufacturing Com- PrimaryExaminerbouis R. Prince pany Limited, Kanagawa-ken, Japan AssistantExaminer-Frederick Shoon [22] Filed July 16 1970 Attorney-Robert E.Burns and Emmanuel J. Lobato [21] Appl. No.: 55,367 [57] ABSTRACT Adevice for monitoring a fluid pressure system com- [30] ForeignApplication Priority Data prises a plurality of tranducers forindividually detecting local temperatures at a plurality of locations inthe April 21, 1970 Japan ..45/33485 system and providing correspondingelectric Signals a 52] U S C] 73/168 73/341 73/342 scanner foraddressing the electric signals in ac- 51 3 315/25 324/73 cordance witha prescribed program and providing 340/324 corresponding output signals,a linearizer for calibrat- [51] Int Cl Golk 7/00 Golm 9/00 ing theoutput signals, an AD converter for converting 58] Fie'ld 68 339 i 339 A340 the calibrated output signals into corresponding digital 73/341 5 5R 2 signals, and means for visually displaying both a tem- AR 6 3 5 1315/25 perature characteristic pattern developed from the 4/73 R,lib/324 digital signals and a temperature reference pattern indicativeof the acceptable temperature levels in the system whereby a comparisonof the two patterns may [56] References cued be made to determinedefective components in the UNITED STATES PATENTS fluid Pressure y2,963,652 12/1960 Taylor et al ..324/73 X 5 Claims, 5 Drawing FiguresTEMPERATURE IN "C 5 MONITORING POINT PATENTEUHETZMQYZ I v I 3.699.810

SHEETZUFZ TEMPERATURE DIFFERENCE IN (3 INTERNAL LEAKAGE IN /min I00 I 00I00 TEMPERATURE DETECTORS L I I m DC AMPLIFIER I 3 -L|NEARIZER PROCESSORl O 5 O 6 *REFERENCE TNPUT SOURCE T O 7 D|SPLAY SCREEN DEVICE FORMONITORING A FLUID PRESSURE SYSTEM.

The present invention relates generally to an improved device formonitoring a pressure system, more particularly relates to a novelmonitoring technique of a pressure system composed of at least onehydraulic pressure component through analysis of thermal characteristicsof the system in relation to a given standard thermal reference.

The present invention is particularly applicable to the monitoring of ahydraulic pressure system such as employed in an aircraft installationand, is more advantageously, utilized in air-bome (on board aircraft)monitoring systems for aircraft installations. Therefore, the followingdescription will be mainly focussed upon the application of the art tothe case of an aircraft installation and its maintenance.

Aircraft installations such as a utility system, flight control systemand/or other system of an aircraft are known to include varioushydraulic components, whose malfunctions are usually caused by internalleakages, external leakages and failure of the parts. Among threecauses, the external leakage and the failure of the parts of thehydraulic components can be monitored through external visualobservation of the mechanism. However, the internal leakage of acomponent cannot be found unless the component is removed from thesystem and subjected to a bench test.

In this connection, the conventional maintenance work of the aircraftinstallation is generally performed following maintenance with areplacement schedule, in which technique a fixed time between overhaulis applied to the respective hydraulic components. When the operationperiod of some hydraulic component after an overhaul comes to the end ofthe time between overhaul, that component is removed from the system forthe next overhaul regardless of its actual functional condition.

This conventional maintenance system is based on the conventionalconception of the failure rate-time after overhaul relationship. Thisrelationship is generally given in the form of a reliability curve,which curve is more popularly called as a bucket curve. In theconventional conception of the relationship, the reliability curve issupposed to show a sudden fall'in the initial failure rate zone, ahorizontal saturation in the random failure rate zone and a sudden risein the wear-out failure zone. In the case of the above-mentionedmaintenance on the basesof a replacement schedule system, the end of thetime between overhaul is so selected as to fall on the termination ofthe random failure rate zone. So, if maintenance on a replacementschedule system is employed in the maintenance of an aircraftinstallation, all the components are thought to be replaced with newcomponents before the time failure of the component is markably andundesirably increased.

In this connection, however, a frequent replacement of the hydrauliccomponents is accompanied with various drawbacks from the view point ofboth maintenance and economy.

Replacement of a component from a system thereof is known to oftentimescause the problem of residual stress on the remainder of the relatedparts of the system and such residual stress is liable to invite laterdevelopment of cracks on the remainder of the system.

So, the more the frequency of the replacement of the component orcomponent from a system, the larger the possibility of later developmentof undesirable cracks on the related remainder components of the system.

As above-mentioned, in maintenance with a replace ment schedule, thehydraulic components are replaced regardless of the actual functionalcondition thereof. Therefore, there is a case when even a component ofperfect functional. condition is subjected to replacement and subsequentoverhaul. This is a loss of time and a loss of work.

Further, in the conventional technique of monitoring, the hydrauliccomponents removed from the system has to be disassembled for checkingthe internal failure, such as wearing out, of the internal parts. Suchtroublesome work naturally results in increasing or extending timenecessary for the maintenance work.

In the aircraft transportation business, the economy in the business isusually evaluated by the ratio of the downtime cost with respect tomaintenance cost. In the case of conventional size aircraft this ratiois in a range from 1.0 to 2.0. However, in the case of aircraft ofextraordinary size, such as a jumbo jet plane, this ratio is known to bein the range from 2.7 to 4.3. So, with recent developments in the sizeof aircraft, there is a strong desire in the aircraft transportationbusiness to find out a way to decrease this ratio at least to the extentof the aircraft of ordinary size. For this desired decrease of theratio, it is necessary to bring about a considerable decrease in thedowntime cost, namely the length of the downtime of the aircraft.

One of the solutions may be provided by extending l the time betweenoverhauls and another solution may be provided by undertaking themonitoring of the component in the air-bome system.

In this connection, the recently developed investigation of theabove-described reliability curve has revealed that the failure ratecurve does not actually show a sudden rise even in the wear-out failurezone. This implies that there is no need of selecting the end of thetime between overhaul so as to have it fall on the termination of therandom failure zone and that the hydraulic component may be perfect inits function even in the wear-out failure zone. From this newly obtainedresult of the analysis of the reliability curve, it can be deduced thata hydraulic component of the aircraft installation needs not be removedand subjected to overhaul oven at and after the end of the time betweenoverhaul, provided that only the monitoring of its function ispertinently performed. This conception has brought about a new techniqueof aircraft maintenance popularly called as the on condition maintenancesystem.

In this new maintenance system, the function of the hydraulic componentsof an aircraft installation can be monitored without removing thecomponents from the systems on the aircraft or, it the component itselfis removed from the system on the aircraft, without disassembling thecomponent itself. Only when the malfunction of the component itself isconfirmed, is the component or the assembly of components subjected tooverhaul work.

One of the typical examples of this on condition maintenance system isfound in the TARAN system employed by United Air Lines, TARAN meaningtest po'rtation business. I

and replace as necessary. In this maintenance system, a particularinstallation or system of an aircraft, for example a landing gearsystem, is disengaged from the usual pressure circuit and a TARAN TESTERcomprising a hydro-pump and flow meters is inserted into the systemscircuit. In this technique, the particular system s circuit can beisolated from its related installation parts and the functionalcondition of the system as a whole can be monitored without removing thesystem from the aircraft. The monitoring of the function in thistechnique is empirically known to be performed with success at aprobability of about 70 percent. However, firstly, although a particularsystem of the aircraft installation can be isolated regarding thefunctional condition from its related parts of the installation in thistechnique, individual components or assembly of the componentsconstruction in the system cannot be isolated in this technique. Thismeans that the functional condition of the individual component can notbe monitored successfully through application of this technique.Secondly, this technique cannot be applied to an air-borne-system.

Therefore, there has been no attempt to develop a maintenance techniquewhich can successfully ascertain a monitoring technique applicable toair-bornesystems and a monitoring system performable without removal ofthe individual hydraulic components from a hydraulic or pressure systemof an aircraft installation.

A principal object of the present invention is to provide a device formonitoring a pressure system composed of at least one pressure componentwithout removing the component or components from the system.

Another object of the present invention is to provide a device formonitoring a pressure system capable of checking internal failures of acomponent in the system without disassembling the component.

Still another object of the present invention is to provide a monitoringdevice for a pressure system advantageously applicable to aircraftinstallation maintenance with successful prolongation of the timebetween overhaul of the components.

Still another object for the present invention is to provide amonitoring device of a pressure system capable of ascertaining successin an on condition maintenance system in aircraft installationmaintenance work.

Still another object of the present invention is to provide a monitoringdevice for a pressure system capable of ascertaining success in theemployment of an airborne-system in the aircraft installationmaintenance.

Still another object of the present invention is to provide a monitoringdevice for a pressure system capable of, when employed in aircraftinstallation maintenance work minimizing the ratio of downtime cost withrespect to the maintenance cost in the aircraft trans- In order toachieve the above-recited objects, in the monitoring system of thepresent invention, local thermal conditions of a component orcomponents, after a preset time operation thereof, are detected bytransducer means disposed at selected points substantially along apressure circuit passing through the component or components of thepressure system and are connected into corresponding electric signals.Next, the

electric signals'are scanned by a scanner and resultant sequential pulsesignals, which, after DC amplification and calibration, are applied toan AD converter for analogue-digital conversion. The digital signals,obtained are, via a processor, displayed in a form of a thermalcharacteristic pattern on a display screen together with a thermalreference pattern resulting from reference inputs to the processor. Whendeviation of the thermal characteristic pattern from the thermalreference pattern is recognized, the component or components are removedfrom the system for replacement.

Other features and advantages of the present invention will be made moreapparent from the ensuing description, reference being made to theaccompanying drawings in which;

FIG. 1 is a fragmentary sectional view of an embodiment of an apparatuswherein the device of the present invention is employed,

FIG. 2 is a graphical representation of a display on a display screenused in the device of the present invention,

FIG. 3 is a fragmentary sectional view of another embodiment of thearrangement wherein the method of the present invention is employed, 7

FIG. 4 is a graphical representation of a display on a display screenused in the device of the present invention,

FIG. 5 is a block diagram illustrating a typical arrangement of thedevice of the present invention.

Referring to FIG. 1, there is shown an embodiment of an arrangementwherein the device of the present invention is employed. In theapparatus 11, two correlated hydraulic pressure components are provided,one being a piston cylinder 30 and another being a spool valve 14. Thepiston cylinder 30 is provided with a piston 12 reciprocable therein apiston'rod 13, one end of which is fixed to the piston 12 and anotherend of which is related to an external driving mechanism, not shown, tobe driven reciprocably thereby. The cylinder 30 slidably encases thepiston 12. The spool valve component 14 is provided with a conduit 19having an opening 18 to an internal cavity or chamber 31 thereof andanother conduit 22 having two openings 20 and 21 to the internal chamberor cavity 31. Both conduits 19 and 22 are connected to a hydraulicpressure source, not shown. The cavity 31 is provided with a pair ofspool valves 32 reciprocable therein and fixedly mounted on a spoolvalve rod 15 externally connected to an operating source, not shown. Thepiston component or cylinder 30 and the spool valve component 14 areinterconnected by two oil paths 16 and 17 opening on opposite sides ofthe piston when the piston is intermediate thereof. In theabove-explained arrangement, temperature detectors 1 to 6 are located atselected points substantially along the advancing path of the oil asshown in the drawing.

In the above-described arrangement, when the spool valve 32 is providedwith a reciprocal movement in the cavity 31 of the spool valve component14, the pressure oil will be introduced into the cylinder component 30and this effects the reciprocal movement of the piston 12 and therunning of the arrangement is effected. The subsequent continuousrunning of the arrangement will cause a temperature change in thevarious parts thereof and this temperature condition is. detected at theselected points by the temperature detectors 1 to 6.

By using the device later explained in detail, thusly monitoredtemperatures are displayed in a form of a curve 42 visually displated ona display screen as shown in FIG. 2, wherein the monitoring points areplotted on the abscissa whereas the monitored temperatures are plottedon the ordinate. As already described, the screen is provided with areference temperature pattern 40 with its tolerance limits 41. When thecurve 42 falls outside the tolerance limits 41, the monitoring pointcorresponding to such portion of the curve is regarded as abnormal inits function. For example, in the case shown, a part of the curve isoutside the permissible limits in this case the monitoring points 4 and5 are found to be out of order, that is the readings taken through thecorresponding openings 20 and 21 are found to be out of order. When thismalfunction is confirmed, the arrangement is removed from the entiresystem to which the arrangement is attached and is subjected tooverhaul.

Another embodiment of the arrangement wherein the device of the presentinvention is employed is shown in FIG. 3. In this case, the arrangementis composed of a piston component 50 only. The piston component 50includes a cylinder 51, a piston 52 reciprocable in the cylinder 51, apiston rod 53 one end of which is fixed to the piston 52 and another endof which is connected to a not shown external mechanism to be operatedthereby and a pair of oil paths 58 and 59, each having an opening 54 and55 to the chamber of the cylinder 51. The openings 54 and 55 areprovided with temperature detectors 56 and 57, respectively. After apreset time of operation of the arrangement, the temperature differencebetween the points 56 and 57 are 7, shown in a form of a visible plot onthe display screen shown in FIG. 4, wherein the temperature differenceis plotted on the ordinate whereas the internal leakage magnitude isplotted on the abscissa. As already mentioned, the screen is providedwith a temperature difference reference pattern 60 with an allowableinternal leakage limit 61.

When the monitored temperature difference plot falls beyond theallowable limit point 62, which is given as the cross point of thepattern 60 with the limit 61, the arrangement is regarded as abnormal inits function and is subjected to removal from the entire system to whichthe arrangement is attached for replacement purposes.

As is mentioned above, it is desirable in the art of the presentinvention to interpret the monitored thermal magnitude into a visiblepattern on a given display screen in an electrical manner together withthe thermal reference pattern. Some practical examples for effectingthis interpretation will be explained in the following description.

Referring to FIG. 5, a typical arrangement for effecting theabove-mentioned interpretation is shown.

The temperatures of the selected points are detected by temperaturedetectors 100 and converted into corresponding electric signals. Thetemperature detector may be constructed in the form of a thermoelectriccouple, a bridge circuit or an infrared temperature detector. Theobtained electric signals are simultaneously introduced into a scanner101 for addressing in a prescribed sequential programme. The outputsignal of the scanner 101 is brought, via a DC amplifier 102, into alinearizer 103 for calibration purpose. The calibrated analogue signalsare converted into corresponding digital signals by passing through anAD converter 104 connected to the linearizer 103. Thusly obtaineddigital signals are applied to a processor 105 for comparison with thereference input supplied from a reference input source 106 connected tothe processor 105. The

output signal of the processor 105 corresponding to the monitoredtemperatures together with those corresponding to the reference inputare supplied to a display screen 107 for a visible display purpose.

The output signals of the processor 105 may be brought into a pertinentmemory device such as a magnetic taping device for a data recordingpurpose. The output signals of the processor 105 may be used for directvisual indication of a good or no good condition, for example byindicator lamps.

By inserting a digital timer into the arrangement in a known manner, themonitoring can be performed periodically with desired intervals.

What is claimed is:

1. An improved device for monitoring a pressure system composed of atleast one pressure component comprising; in combination,

a. transducer means for detecting local thermal conditions within apressure circuit passing through a pressure component and convertingthem into corresponding electric signals and disposed at selected pointsalong the pressure circuit through said component, of a pressure system,

b. a scanner connected to said transducer means for addressing saidelectric signals following a prescribed sequential programme,

0. A DC amplifier connected to amplify the output of said scanner,

(1. a linearizer connected to said DC amplifier for calibrating theoutput signals of the amplifier,

e. an AD converter connected to said linearizer for converting outputsignals of the linearizer into corresponding digital signals,

f. a processor connected to said AD converter and receptive of saidoutput digital signals, a reference input source connected to saidprocessor and a display screen connected to said processor fordisplaying a thermal characteristic pattern composed of said digitalsignals simultaneously together with a thermal reference patterncomposed of said reference input for comparing the patterns.

2. An improved monitoring device of claim 1, wherein said transducermeans comprises thermoelectric couple means.

3. An improved monitoring device of claim 1, wherein said transducermeans comprises a bridge circuit.

4. An improved monitoring device of claim 1, wherein said transducermeans is an infrared temperature detector.

5. An improved monitoring device of claim 1, further comprising adigital timer for performing the monitoring operation periodically atdesired intervals.

1. An improved device for monitoring a pressure system composed of atleast one pressure component comprising; in combination, a. transducermeans for detecting local thermal conditions within a pressure circuitpassing through a pressure component and converting them intocorresponding electric signals and disposed at selected points along thepressure circuit through said component, of a pressure system, b. ascanner connected to said transducer means for addressing said electricsignals following a prescribed sequential programme, c. A DC amplifierconnected to amplify the output of said scanner, d. a linearizerconnected to said DC amplifier for calibrAting the output signals of theamplifier, e. an AD converter connected to said linearizer forconverting output signals of the linearizer into corresponding digitalsignals, f. a processor connected to said AD converter and receptive ofsaid output digital signals, g. a reference input source connected tosaid processor and h. a display screen connected to said processor fordisplaying a thermal characteristic pattern composed of said digitalsignals simultaneously together with a thermal reference patterncomposed of said reference input for comparing the patterns.
 2. Animproved monitoring device of claim 1, wherein said transducer meanscomprises thermoelectric couple means.
 3. An improved monitoring deviceof claim 1, wherein said transducer means comprises a bridge circuit. 4.An improved monitoring device of claim 1, wherein said transducer meansis an infrared temperature detector.
 5. An improved monitoring device ofclaim 1, further comprising a digital timer for performing themonitoring operation periodically at desired intervals.